System for parallel operation of alternators



p 1931. J. L. FINCH 31;

SYSTEM FOR PARALLEL OPERATION OF ALTERNATORS Filed Feb. 16 1925 2 Sheets-Sheet 1 Fig.1

6' REM) 1175/ 7/0 I I I I I I I DPE/l TIME INVENTOR as L. rmcn Sept. 8, 1931. J. FINCH SYSTEM FOR PARALLEL OPERATION OF ALTERNATORS Filed Feb. 16, 1925 2 Sheets-Sheet 2 LET -: the teinlencv oi the alternators lo hunt.

Patented Sept. 8, 1931 UNE'E'ED STATES E ATEN'E' ()FFICE.

JAB'IES L. FINC'H, OF NEW YQRK, N. Y., ASSEGNOE TO BIT-.1310 CORPORATION OF AMERICA, A CORPORATIGN OF DELAWARE SYSTEM FOR PARALLEL OPERATION OF ALTERNATORS Application filed Februazy This imientimi concerns the operation of high frequency alternators in parallel providing means for obtaining a large synchronizing torque and avoiding to a large extent The has been let l particularly parallel operation of alternators of the shown in the ll. S. patents to Alexnndeison 1.008,?)77, l.ll0.029 and 1,110,030 but is, oi course, not limited to the particulnr case of allernators of this type.

hie object 01" the invent mi is to provide a system for operating alterna tors in parah lel providing for a large synchronizing torque.

Another object of the invenlion is to provide a system tor parallel operation of ail'ernators whereby hunting is reduced to a large extent.

Another object ol' the invention is to provide an a rrangenisnt for the parallel opera lieu of alternaiors providing a large synchronizing torque and tendii'ig to dain icn hunting oscillations quickly.

Still another object of the invention is to provide an arrangement for he operation or in parallel whereby during hunting oscillations the syn '-.hronizing torque will be increased as the phase angle between the alter-suitors increases and will. he reduced as the phase angle between the alternators decreases.

Still anz'ither object of the invention is to provide a system for the ruieration of alternators in parallel whereby the synchronizing torque tending to hold the alternators in phase during luinting oscillations will be greater than the. synchri'inizing torque tending to bring them back into phase.

Still anolher object of the invention is to provide an impedance in the circulating circuits o? alterualors operating: in parallel and to provide for short circuiting the llllllCllunce as: the :ill'ernators reach ninrcin'uun out oi phas position during hunting oscillations.

In many high power radio communicaions it is very desirable to operate .y of high trequency alteruators in The altcrnators in use for this arra ngenie useful in the parallel.

Serial No. 9,537.

purpose ha re a frequency of from 15,000 to 50.000 cycles per second. This high frequency in itself does not present any special problems in parallel operation but the machines usel'l in such installations have a very high internal reactance and resistance and hese features do introduce special problems in the parallel operation. The high internal r act nee cuts down the circulating current l therefore the synchronizing torque considerahly and it is, therefore, necessary to provide means for neutralizing this react- :incc. T his is done under the present arijhlllll by placing a condenser of the ioper rating in series with each alternator ahead of its paralleling connection. Witht such condensers the circulating current would attain a. maximum of only 35 percent of full load current and a power interchange of only about 10 percent of full load power at the niosi: critical phase angle. Then the condensers are used and. adjustment is made for the highest possible power interchange its value at the most critical phase angle is about twice full load power. This is, of course, not a practical condition since practically the whole power output of the machines would be absorbed in the internal resistance of the machines themselves but by properly dimensioning the condensers the power interchange can be made of the des red value. The preferred arrangement is to provide for a power interchange of about 25 percent of the full load power.

(Then such high frequency alternators are operated in parallel there is a decided tende': y for hunting between them as is the use under re. ..in conditions with synchronous machines at power frequencies. There seem to be many conditions which tend to produce hunting in the case of high frequency alternators under telegraphic load "and they seem to vary with the individual nsliallatious and even to change frequently n the same installation. The latter is probblv due to certain variations in the power in the drivin motors and is robabl due to certain torque harmonics which do not coincide in the two motors.

A second source of vaaarions hunting is f und in the tale The keying is usually 1. tally so that the inipu regularity.

Since the motor in'uit and the alternator output cannot l e exactly baianced under both conditions o' lo a lend ency to hunt is produce and u :eyinq; speed corrcspoinls to ti: huntuniting will all-crnators would corrccti v e ing between the alterna tend to build up 2' drop out oi" step were taken.

Similarly any initial hunting woul; tend to increase under 'l'zworable co: ions of i 103 hi] l IfS key in; due to the fact 1' at the mg torque is not the same wt as with the key closed cit the antenna loaal. (in

torque drawing the llit i' lillifi might be greater l time car straining them from opposite direction, thus. c. ,.u in hunting.

A third source of hu 7 irregularity of the due to inexact spar rotor or to an irreg; that the rotor passes throng; larities cannot be entirely chin f chines with such a large nun as are required to produce t quencies. Thus the ma; rotor position and lllllitdig may res; c hunting period corresponds to t nator revolutions.

It has been found tl at in tions, even when all loan taken to lrecp the alternatri, in step. the

conditions 0t hunting are vcrv serious. I he usual hunting: in

i such bi two practna ll while no hunting taking pun-c asn during hunting while the phase angle between the alternator-s is increasing, tl getting the higher value of synchronizing torque. lut when the pl angl is decreasing the relay ll open the short circuit and place the inductance in the circulating circuit thus the lower value of torque until the i "heir iii-phase position at which time 2138 inductance will again be short which the synchronizing torque of alternaiting in parallel may be increased,

sihematic arrangement by which 'lhe hunring oscillations of alternators operating in parallel may be quickly dampened,

lfig. Z5 is a dia 'rani oi a complete circuit zn'rznigrcnient tor re operation of alternators inauiel according to the invention, and

is a group of comparative curves illustrating the operation of the device tor I l out hunting oscillations.

"lug now to Fig. 1, in which very simple schemati arrangement I sing the synchronizing torque betncen zziternators operat. in parallel, A and A represent two alternators in parallel ha dug internal iinluctances represented by L and L This inductance, in machines 0? the type under discussion, is ordinarily large enough to cut down the circulating current and therefore the synchronizing torque consim rably below the value necessary to keep the alternators in step. The eli'ect of this internal inductance is neutral izcd by 11 'ing the condensers (l and C in series pith the alternators, thereby correcting the power factor in the circulating circuit I Q Q L and causing larger circulating current to flow. By correctly dimensioning the condensers C and (7 this circulating current may be adjusted to the desired value.

Fig. 2 illustrates the method of dampening hunting oscillations in alternator-s operating in parallel. For the s: lre of clcarness all circuits and devices have been omitted from this figure except the circulating cir cnit and the device S and circuits necessary to (la upon the hunting oscillations. A and A: represent alternator-s operating in parallel and cross connected through the circuit A conductor 12', conductor 13f). alternator A and conductor 140. In the tie ci'miprising the conductors 138 and 13-9 is placed an inductance 131 which under certain conditions explained hereinafter will be short circuited by the contacts 0 relay" 1352. Across the alternators A A are coiinested transformers 12S and 12% respectivc ly, having their secondaries connected in series so that when the alternators are in phase the voltages in these secondaries will neutralize each other. In circuit with the series connected secondaries are the resistance 136 and the rectifier 130. One terminal of the resistance is connected to the coil of polarized relay 133 to the other terminal of which is connected one plate of the condenser 135. The other plate of this condenser is connected to the opposite terminal of resistance 136.

lVhen hunting begins and the alternators start to get out of phase with each other, the voltages in the secondaries of the trans formers 128 and 129 will no longer balance and rectified current will begin to flow through the resistance 136. This current will increase in value as long as the phase angle between the alternators is increasing and likewise the voltage across the resistance will increase. This increasing Voltage charges the condenser 135. The polarized relay has its armature slightly biased so that its contacts will remain open as long as there is no voltage across the resistance 136 and as long as the voltage is increasing. lVhen the aiternators begin to swing back into phase the voltage across this resistance begins to decrease, the condenser 135 begins to discharge and sends a reverse current through the polarized relay 133 causing it to open its contacts. These contacts will remain open as long as the voltage across resistance 136 is decreasing and therefore as long as the phase angle between the alternators is decreasing. When the phase angle reaches zero and starts to increase in the other direction an increasing current will again flow through the resistance 136 causing condenser to charge and the polarized relay 133 to open its contacts.

The contacts of the relay 133 control a circuit comprising a source of energy B and the relay 132 whose contacts serve to open and close a short circuit across the inductance 13 The relay 132 has its armature so biased that long as there is no current flowing through the relay coil the contacts will be open but when current flows through the relay coil the contacts will close. he inductance 131, when it is in circuit, serves to cut down the circulating current and therefore the synchronizing torque considerably. When, during hunting oscillations, the phase angle between the alternators is increasing in either direction the voltage across resistance 136 will be increasing, the relay 133 will hold its contacts open, the relay 132 will hold its contacts closed and a heavy circulating current will flow between the alternators. This heavy circulating current will persist until the alternators reach their maximum out 0? phase position. hen the phase angle between the alternators begins to decrease the voltage across the resistance 136 will decrease and condenser 135 will discharge, thereby causing relay 133 to close its contacts, which in turn will cause the relay 132 to open its contacts, thereby removing the short circuit around inductance 131 and inserting the inductance in the circulating circuit. This causes the circulating current and therefore the synchronizing torque to decrease. It will thus be seen that as long as the phase angle between the alternators is increasing a large synchronizing torque will be effective to oppose the change. After the phase angle has reached its maximum and begins to decrease a lessened synchronizing torque will be effective and there will, therefore, be a lessened tendency for the alternator armatures to swing past their mean position.

These effects are clearly indicated in the group of curves shown in Fig, 4 in which A represents the circulating current, B represents the phase relation between the alternators and C represents the position of the relay 132, all plotted against time. It will be noted that as the phase angle increases, that is as the curve B rises, the circulating current represented by A will increase until the phase relation reaches a maximum when, owing to the insertion of the inductance 131 in circuit, the circulating current will suddenly drop from the point P to the point Q. The conditions for the lesser circulating current persist until the generators come in phase at the point C when the relay 132 will again close its contacts, short circuit the inductance 131 and allow the circulating current to increase in the opposite direction to the point P which represents the maximum out of phase position of the alternators in the other direction. At this point the relay 132 again opens its contacts and inserts the inductance 131 in the circulating circuit and the circulating current is again reduced from the point P to the point Q. This action is repeated at each maximum out of phase position and the hunting oscillations quickly die out as indicated by the curve A. Due to imperfect machining of the alternators their respective voltages would not be constant. These voltages if plotted with respect to time would show a pure sine wave and a series of harmonics interposed thereon. These harmonics which are of higher frequency than the hunting frequency of the alternators would cause the armature of the relay 133 to chatter. A condenser 134 is shunted across the relay winding to by-pass these harmonics so that the relay responds only to the dilterential voltages caused by hunting. Condenser 134 also serves as a by-pass for radio frequencies and insures greater output for the rectifier.

Fig. 3 shows a complete circuit diagram illustrating the use of the devices illustrated schematically in Figs. 1 and 2 in connection with a standard radio telegraph installation. Certain difficulties in connection with the keying in such a system prevent the use of the simple connections shown in Figs. 1 and 2. The operation of keying essentially reduces the alternator voltage to a very low value when the key is open. It is clear, therefore, that under such circumstances the circulating current and therefore the synchronizing torque would drop to a very small value whenever the key were opened and it would, therefore, be very difiicuit to keep the alternators in step. To avoid such difficulties the simple arrangements in Figs. 1 and 2 have been modified to some extent as shown in Fig. 3. The principal of their operation, however, remains exactly the same as in the simple devices described above.

In this figure the antenna 3 is fed by means of two alternators 1 and 2 represented diagrammatically as of the Alexanderson type. The armature coils of these alternators feed the primaries of transformers 6 and 7 which are coupled to secondaries 8 and 9 in the two branches of the antenna circuit. The operation of keying which carried out by means of the key 150 in circuit with a source of power 151 causes portions 10 and 11 of these secondaries to be short circuited intermittently by means of magnetic amplifiers shown diagrannnatically at 16 and 17. These amplifiers are of a well known type and consist of iron core inductance coils with saturating coils 45 and to controlled by the contacts 18 and 19. is indicated in the drawings when key 1:30 is open contacts 18 and 19 are in the closed position. With these contacts in closed position the cores of the amplifiers are magnetically saturated, owing to the flow of direct current from the batteries 20 and 21, thus reducing he inductance of the magnetic amplifier coils. In this position the magnetic amplifier together with the condensers 1e and 12 form practically a short circuit across the cores 10 and 11 of the transformer secondaries. lVhcn key 150 is closed the contacts 18 and 19 are open the current in the saturated coils 45 and 46 is ii'iterrupted the inductance of the amplifier coils rises and the path including the amplifier presents a high impedance to the low of current from the transformers. The altcrnators thereupon impress a higher voltage upon the antenna circuit. The difference in the power supplied to the antenna in the key open and the key closed positions permits the radiation of signals from the antenna.

One armature coil in each alternator designated respectively as 22 and 23 is segregated, that is, it is not used in the feeding circuit. These coils through the transformers 28 and 29 operate a phase dampening device similar to that described above. As these coils are not included in the feeding circuit it is obvious that their voltage is independent of the load on the alternators. These same coils may be used for the purpose of regulating the driving motor speed in the manner expained in U. 3. patent to AleXan-derson 1,l( \),8-l7. T he secondaries of transformers 28 and 2:) are connected through the rectifier 30 \YlLll the resistance 36 which have the same functions as the rectifier and the resistance 136 in Fig. Across the resistance 36 are connected in series the polarized relay 33 and the condenser 35, the operation of which is exactly anal gens to the relay 133 and the condenser of Fi The relay 33 is shunted by condenser 31-, the purpose of which is the same as the condenser 13% of Fig. 2.

The secondaries of the transformers 8 and 9 tied together by a circuit comprising conductor 38, condenser 12, conductor l0, inductance 31 with its short circuiting contacts, conductor -11, condenser 13 and conductor The condensers 12 and 13 in this circuit correspond to the con-- deuscrs C and C in Fig. 1 and their action in increasing synchronizing torque is the same as that explained above in connection with that figure. These condensers also serve part of the capacity for neutralizing the inductance of the magne'ic amplifiers 1t; and 17, that is, in the 1nescnt case the single condenser usually used to neutralize he magnetic amplifier inductance is replaced by the two condensers 123 and 1-l connected with the magnetic amplifier 16 and the two cond nsers 13 and 15 connected with the magnetic amplifier 17. The short circuiting contacts of the inductance 31 are cmitroileil by a biasing spring and a polarized relay 32 whose coil circuit which composed of a variable ltSi', .ance 37 and source oi" power controlled in turn by a biasing spring 43 and a polarized coil 33 in a manner entirely analogous to the simple device shown in Fig. 2. As long as the ma chines are exactly in phase the voltages of the transformers 28 and 25) will balance each other and there will be no flow of current through the resistance 36. When hunting oscillations commence the phase angle between the machines begins to vary, the voltages of the transformers 23 and 29 are no longer balanced and rectified current begins to fiow through the resistance 36. This rectified current increases in value the phase angle increases. As long as the voltage drop across the resistance 36 is increasing, due to the increasing ciu'rent, condenser 35 will be charging and the relay 33 will hold its contacts open, thereby deenergizing the control circuit of relay 32 and permitting the short circuiting contacts across the inductance 31 to remain closed. As long as the phase angle is increasing, therefore, the synchronizing torque will have a large value. The circulating currentin this case flows through conductor 38, condenser 1Q, conductor 40, closed contacts of relay 32, conductor 41, condenser 13 and conductor 39. lVhen the alternators reach their maximum out of phase position and start to swing back into phase the (litterence in the voltages in transformers and 29 will decrease and the rectified current in resistance 36 and therefore the volta e across this resistance will decrease. Condianser 35 will then discharge through the coil of polarized relay 33 causing it to close its contacts and energize the coil of relay 32. The latter will open its contacts and remove the short circuit around the inductance 31 and the circulating current from which the synchronizing torque results will thereupon have to flow through inductance 31. Its value will, therefore, be reduced and the synchronizing torque will likewise be smaller. This action will. be repeated every time the machines leave their out of phase position and reach a maximum. thereby quickly dampening out the hunting oscillations as explained in connection with Fig. l above and shown graphically in Fig. 4.

Loading coils 4 and 5 are placed in the two branches of the antenna circuit to cut down the value of circulating current in the path connecting the alternators to the antenna as obviously if this were a low impedance path the circulating current would flow through it in preference to the tie including inductance 31.

It will be noted that the usual single blocking condenser in the magnetic ampli licr circuit has in this case be n replaced by two, namely the condensers l2 and These two in series have the same capa -ty as the single condenser usually for this purpose and in addition the condenser 12 serves to increase the circulating current between the machines. This utilization of parts of the magnetic amplifier circuits as portions of the tie circuit is an important feature of the invention it simplifies circuit connections considerably and effects a large saving in the amount of apparatus which would otherwise be ncces:-;ary in connection with the keying circuit.

it is, therefore, apparent that the invention provides a very simple device i'or quickly damping out hunting oscillations in the operation of alternator in parallel. unique feature of the arrai ment is it is HHDOOGSSZHy to synchromze the al' nators before closing the tie switch. "his switch may be closed regardless of the phase relation as the maximum current is less than the load current of the alternators and no harm is done by thus connecting it. The resulting hunting is quickly dampened for by an anti-hunting device.

Although the device has been explained in connection with a certain type of alternator it is obvious that this alternator is not an essential element of the system. The system can be used with alternators of different types. It is moreover obvious that. numereus keying and circuit arrangements wil readily suggest themselves to those led in the art. For example, a single keying circuit could be used for both alternators. The system shown is given merely by way of example and not in a limiting sense.

Having described my invention what I claim is:

1. The combination of a plurality of alternators in parallel, a tie circuit between said alternators, means in said tie circuit for damping hunting oscillations in said alternators and means operated by said alternators to control said damping means.

2. The combination of a plurality of alternators in parallel, a circuit connecting said alteri'iators, an impedance in said circuit, means for short circuiting said impedance and means responsive to change in di-. rection of variation of phase angle between said alternators to control said short circuiting means.

2 The combination of a plurality of alternators in parallel, a circuit connecting said alternators, an impedance and means responsive to change in direction of variation of phase angle for inserting said impedance in said circuit when the phase angle between said alternators is decreasing.

4-. The combination of a plurality of alternators in parallel, means responsive to change in direction of variation of phase angle between said alternators for increasing the syncl'ironizing torque between said al ternators when the phase angle between them is increasing and for decreasing the synchronizing torque when the phase angle is decreasing, and means to control said first named means. i

5. The combination of a plurality of alter nators in parallel a circuit connecting said alternators, means for changing the impedance of said circuit when the direction of variation ot the phase angle between said alternators changes and means to control said first named means.

6. The combination of a plurality of alternators in parallel. means for changing the synchronizing torque between said alternators when the direction of variation of the phase angle between them is changing and means associated with the alternators for controlling said first named means.

7. The combination of a plurality of alr LL .for increasing the synchronizing torque to the char in and dischargin currents ii ternators in parallel and means responsive to hunting oscillations in said alternators increases and for decreasing the L-fJI1(l11OillZ-- ing torque when the amplitude of hunting oscillations decreases.

8. The combination of a plurality ct alternators in parallel and means responfi to hunting oscillations for developing synchronizing torque as long as the phase angle between said alternators is increasing and means for reducing the synchronizing torque while the phase angle is decrea'ing.

9. The combination of two alternators connected in parallel, a circuit connecting said alternators, a variable impedance in said circuit, means for varying said nput ance including a control circuit d fferentially connected to said alternators.

10. The combination of two alternators connected in parallel, a circuit connecting said alternators and including a variable impedance, means for varying said impedance including a control circuit difi'erentially connected to said altern:

trol circuit including a rectifier and an in .pedance and means responsive to ch; ring voltage across said impedance for varying said variable impedance.

11. The combination of two alternators connected in parallel. a circuit conne'ting said alternators including a variable impedance, a control circuit differentially connected to said alternators including a rectifier and an impedance, a condenser connected across said impedance and means responsive to the charging and discharging currents of said condenser for varying said variable impedance.

12. The combination of two alternators connected in parallel, a circuit connecting said alternator-s including a variable impedance, a control circuit differentially connected to said alternator-s including a rectifier and a resistance, a condenser connect d across said resistance and means responsive arisaid condenser, for increasing the variable impedance when the condenser is discharging and decreasing the impocance when the condenser is charging.

13. The combination of two altcrnators connected in parallel, a circuit including an impedance connecting said alternators, a short circuiting device connected across said impedance, a control circuit differentially connected to said alternators including a rectifier and a resistance, a circuit connected across said resistance including a conde ser and electromagnetic operating means for said short circuiting device res 'ionsive to the charging and discharging currents of said condenser.

14. The combination of two alternators connected in parallel, a circuit connecting said alternators said circuit including a condenser and an inductance, a short circuiting device connected across said inductance, a control circuit differentially connected to said alternators, said control circuit including a rectifier and a resistance and a circuit connected across said resistance including a condenser and electromagnetic control means or said short circuitin device responsive to the charging and discharging currents of said condenser.

15. The combination of two altcrnators connected in parallel a circuit connecting said altcrnators including a condenser and.

iernators. means including an imit said tic circuit or damping huntoscillations in said alternators, and means operated by said alternators to control said damping means.

l7. The combinationot a plurality of alteras in parallel, a circuit connecting said alternaiors, an impedance in said circuit, nice for short circuiting said impedance, and means including a relay responsive to change direction of variation of phase angle between said alternators to control said short circniting means.

18. The combination of a plurality of alternators in parallel, a circuit co nccting said alternators, an impedance associated with said circuit. and means responsive to change in direction of variation of phase angle l)-3-- tween said alternators to insert said impedance in the connecting circuit.

19. The combination of a plurality of alternators in iarallel, a circuit connecting said alternators. an impedance in said circuit, and a relay responsive to change in direction of variation of phase angle between said alternators adapted to short circuit said impedancc.

20. A circ it arrangement comprising a plurality of alternators in parallel, a tie circuit between said alternator-s, means including an impedance in said tie circuit and a relay operatively associated therewith for damping out hunting oscillations in said alternators and means for increasing the synchronizirg torque between said alter nators.

21. In a circuit arrangement comprising a plurality of alternators in parallel, a tie circuit connecting said alternators an impedance in said tie circuit, a transformer assoitc-z's in parallel, a tie circuit connect-.-

ciated with each of said alternators and adapted to be energized thereby, a circuit including a resistance and a rectifier connecting the secondaries of all of said transformers, a relay associated With said last named circuit and adapted to be controlled by differential current therein, and short circuiting means associated With said impedance and operated by said relay.

22. The combination of a plurality of alternators in parallel, a tie circuit connecting; said alternators. an adjustable impedance in said tie circuit for damping hunting oscillations between said alternators, and a relay associated with said alternator-s to control said damping impedance.

23. The combination of a plurality of alternators in parallel, a tie circuit connecting said alternators, an adjustable impedance in said tie circuit for damping hunting oscillations in said alternator-s and a relay associated with said tie circuit and operated by said alternator-s to control said damping impedance.

24. The method of damping hunting oscillations between two alternators connected in parallel by a tie circuit of adjustable impedance which includes the step of combining a portion of the current generated by each of said alternators, rectifying the differential component of the combined current, and controlling the impedance of said tie circuit in accordance with variations in intensity oi" the rectified current.

In a circuit arrangement comprising; a plurality of alternators in parallel and a load circuit energized thereby, a tie circuit connecting said alternator-s, an impedance in said tie circuit, means for short circuitinp; said impedance and means including: a circuit operatively interposed between said altcrnators and said short circuiting means to control said short circuiting means.

JAMES L. FINCH. 

